Ambulatory medical devices include implantable medical devices (IMDs), wearable medical devices, handheld medical devices, and other medical devices. IMDs can include cardiac rhythm management (CRM) devices, such as implantable pacemakers, implantable cardioverter defibrillators (ICDs), subcutaneous implantable cardioverter defibrillators (S-ICDs), cardiac resynchronization therapy devices (CRTs), a combination of such, or one or more other devices used to monitor, detect, or treat various cardiac conditions that can result in a reduced ability of a heart to sufficiently deliver blood to a body. In some cases, heart conditions may lead to rapid, irregular, or inefficient heart contractions, such as atrial fibrillation (AF) or one or more other conditions. To alleviate such conditions, various medical devices can be used to monitor heart activity or to provide electrical stimulation to optimize or control contractions of the heart.
Traditional cardiac rhythm management (CRM) devices, such as pacemakers or defibrillators, include subcutaneous devices implanted in a chest of a patient, having one or more leads to position one or more electrodes or other sensors at various locations in the heart, such as in one or more of the atria or ventricles. In certain examples, the one or more leads can include a pressure sensor positioned in the heart and coupled to the CRM device through a conductor in the lead. Separate from, or in addition to, the one or more electrodes or other sensors of the leads, the CRM device can include one or more electrodes or other sensors (e.g., a pressure sensor, an accelerometer, a gyroscope, a microphone, etc.) powered by a power source in the CRM device. The one or more electrodes or other sensors of the leads, the CRM device, or a combination thereof, can be configured detect physiologic information from, or provide one or more therapies or stimulation to, the patient.
In certain examples, IMDs can include diagnostic-only devices, such as implantable loop recorders (ILRs) or subcutaneously implantable heart failure monitors (SubQ HFMs), including one or more sense amplifiers to monitor electrical heart activity within a patient, or one or more sensors to monitor one or more other internal patient parameters. Subcutaneous implantable devices can include electrodes that are able to sense cardiac signals without being in direct contact with the heart. Other examples of IMDs include implantable drug delivery systems or implantable devices with neural stimulation capability (e.g., vagus nerve stimulator, baroreflex stimulator, carotid sinus stimulator, spinal cord stimulator, deep brain stimulator, etc.).
Wearable medical devices can include wearable cardioverter defibrillators (WCDs) or wearable diagnostic devices (e.g., an ambulatory monitoring vest, holter monitor, cardiac event monitor, or mobile cardiac telemetry devices). WCDs can be monitoring devices that include surface electrodes. The surface electrodes may be arranged to provide one or both of monitoring to provide surface electrocardiograms (ECGs) and delivery of cardioverter and defibrillator shock therapy. In some examples, a wearable medical device can also include a monitoring patch worn by the patient such as an adherable patch or can be included with an article of clothing worn by the patient.
Handheld medical devices can include personal data assistants (PDAs) and smartphones. The handheld devices can be diagnostic devices that record an electrocardiograph (ECG) or other physiological parameter while the device is resting in a patient hand or being held to a patient chest.
CRM devices can be implantable, but in some situations may not include dedicated atrial sensing capability. Additionally, some diagnostic-only implantable, wearable, and handheld devices do not include dedicated atrial sensing capability. Patients with these types of devices may develop atrial arrhythmias, such as atrial fibrillation (AF). Knowledge that a specific patient is experiencing AF can be useful to physicians and clinicians for diagnostic purposes or to tailor performance of a medical device to that patient's needs to provide the most effective patient therapy.